This invention relates generally to the tape driving mechanism of a tape recorder for use with a cassette tape, and more particularly, the present invention relates to apparatus for controlling the tension applied to the magnetic recording tape supplied from a tape cassette.
In order that recording and reproducing are effected in a tape recorder with high fidelity, the magnetic recording tape should be in contact with the record/reproduce head or heads in a satisfactory manner. To this end, it is necessary that the tension of the tape is always constant. In a conventional tape driving mechanism of a so called open-reel tape recorder, the mechanical accuracy of various elements in the tape running system is made high or tape tension control device having a mechanical or electrical means is provided so that the running tape exhibits a constant tension all the time.
However, in a tape recorder for use with a compact cassette (trademark), the above-mentioned countermeasures, which have been taken against open-reel tapes, have not been adapted because the way of applying tension is basically different from that of the open-reel type recorders. In a compact cassette, the magnetic tape is guided by guide pins and guide rollers which are made of a synthetic resin and are provided in a narrow casing of the compact cassette. The mechanical accuracy of various elements constituting a part of the tape running system is relatively low when compared with that of the open-reel tape recorders.
In the conventional cassette tape recorders, the tape tension is mainly given by the driving force of the capstan and by the frictional force produced by the slipping of the reel mount of the payoff (supply) reel. Therefore, it is difficult to maintain the tape tension constant. As a result, the tape is apt to vibrate in its longitudinal direction, in the vicinity of the record/reproduce head, causing the occurrence of modulation noise and dropout in the recording or reproducing signal.
Some conventional cassette tape recorders have two capstans positioned upstream and downstream of the record/reproduce head. In such a dual-capstan tape recorder, the rotational speeds of the two capstans are selected so that the rotational speed of the upstream capstan is a little lower than that of the downstream capstan. Namely, tape tension is applied by the slipping friction between the tape and the upstream capstan, which slipping occurs by the difference in rotational speeds between the two capstans. However, such a dual-capstan type tape recorder has suffered from a problem that the speed difference is apt to deviate from a desired value due to secular change. Furthermore, since the tape tension is controlled by the slipping between the capstan and the magnetic tape, the frictional coefficent is apt to change in accordance with the sort of the tape and variation in ambient temperature and humidity, causing the tape tension value to deviate from its optimal value.